1. Field of the Invention
The present invention generally relates to a phase change resistor cell and a nonvolatile memory device using the same, and more specifically, to a nonvolatile static random access memory (hereinafter, referred to as “SRAM”) comprising a phase change resistor and a hybrid switch which does not require an additional gate control signal.
2. Description of the Prior Art
In general, nonvolatile memories such as a magnetic memory and a phase change memory (hereinafter, referred to as “PCM”) has a data processing speed as fast as a volatile Random Access Memory (hereinafter, referred to as “RAM”) and conserves data even after the power is turned off.
FIGS. 1a to 1d are diagrams illustrating a conventional phase change resistor 4 (hereinafter, referred to as “PCR”).
The PCR 4 comprises a top electrode 1, a bottom electrode 3 and a PCM (Phase Change Material) 2 inserted therebetween. If a voltage or current is applied to the PCR 4, the PCM 2 reaches a high temperature state. As a result, resistance is changed, and then an electric conduction state is also changed. Here, AgInSbTe has been widely used as the PCM 2.
As shown in FIG. 1c, if low current having less than a threshold value flows in the PCR 4, the PCM 2 is heated to a proper temperature for crystallization. As a result, the PCM 2 is changed into a crystalline phase, and the PCR 4 reaches a low resistance state.
On the other hand, as shown in FIG. 1d, if high current having more than the threshold value flows in the PCR 4, the PCM 2 is heated at a temperature of over a melting point. AS a result, the PCM 2 is changed into an amorphous phase, and reaches a high resistance state.
As described above, the PCR 4 can store data corresponding to the states of two resistances as nonvolatile sates. In other words, if the low resistance state of the PCR 4 refers to data “1” and the high resistance state of the PCR 4 refers to data “0”, the PCR 4 can store logic values of the two data.
As a result, a nonvolatile memory device of high performance has been required with a high-speed SRAM having rapid memory operation characteristics, a phase change resistor having the above-described nonvolatile characteristics and a hybrid switch which does not require an additional gate control signal.